The present invention relates to endless transmission belts and, in particular, to endless belts for use in continuously variable transmissions of the chain type in which a number of link plates are interconnected in an endless manner.
One example of a conventional endless transmission belt of the above-mentioned type is disclosed in Japanese Pat. Laid-Open No. 99143/1984. According to this disclosure, link plates of the roller chain and the chain belt are each formed with two pin holes, and a number of such link plates are alternately overlapped each other and interconnected by pins in an endless manner.
The construction of the conventional endless transmission belt will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, a transmission chain 1 has sets 2 of link plates 3 in which the link plates 3 alternately overlap each other and are interconnected by round pins (joint members) 4. Each of the round pins 4 is received in the group of aligned openings 5 of the alternately overlapped link plates 3. Holding clips 6 are used to hold the round pins 4 in place.
As shown in FIG. 2, the holding clips 6 are formed out of a metal or plastic material and have a generally C-shaped configuration. When installed, the clips 6 expand into a dimension corresponding to the width of the chain at positions where the round pins 4 form joints. Each clip 6 has a generally linear back portion 7 provided at the center thereof and has a sufficient length to extend across the full width of two sets 2 of alternately overlapped link plates 3. Each holding clip 6 also has a pair of arms 8, each extending from its one end perpendicularly with respect to the back portion 7 and in parallel with respect to the outermost link plates 3 of the two sets 2. Each arm 8 has a free end 9 which engages either the round pin 4 through the sets 2 of link plates 3 or the outer surface of the outermost link plate 3.
A second example of the prior art is disclosed in Japanese patent publication No. 53227/1983 in which link plates are each formed with a single opening and are provided with rotation preventing projecting portions or transitional (recess) portions.
The construction of the second example of the prior art will be described with reference to FIGS. 3 through 11.
Referring to these figures, each link element 11 has a web 12 and an opening 13, the opening 13 being defined by two longitudinal sides 14a and 14b, and vertical sides 15a and 15b joining the longitudinal sides 14a and 14b. The vertical sides 15a and 15b have projections 16a and 16b, respectively, which project toward the center of the opening 13. Each of the projections 16a and 16b connects with the longitudinal sides 14a and 14b via transitional portions 17a and 17b. The link element 11 also has link rolling contact surfaces 18a and 18b, and corners 19a and 19b at the projections 16a and 16b. Pins 20, which cooperate with the link elements 11, each have two head surfaces 21a and 21b which continue, via curved transitional portions 22, with two parallel surfaces 23a and 23b extending longitudinally of the pin 20. The end faces 24a and 24b of each pin 20 are flat, and slots 25 are formed in the transitional portions 22 in the vicinity of these end faces. The slots 25 receive circlips 27 which retain the link elements 11 via washers 27a.
In the transmission chain for use in a transmission having conical pulleys, a plurality of link elements 11, each receiving two pins 20, are linked by pins 20 which extend perpendicular to the faces of the link elements 11 through the openings 13 of the link elements 11. The end faces 24a and 24b of the pins 20 act as frictional surfaces and thus cooperate with the conical surfaces of the conical discs. The parallel surfaces 23a and 23b extending longitudinally of the pins 20 are in rolling contact with the link elements 11, and these parallel surfaces 23a and 23b have a radius of curvature different from that of the rolling contact surfaces 18a and 18b of the link elements 11 which cooperate therewith.
The zone of contact between the vertical sides 15a and 15b defining the opening 13 of each link element 11 and the corresponding parallel surface 23a and 23b of the pin 20 are shorter than the vertical sides 15a and 15b, and that zone is offset, by the transitional portions 17a and 17b of the vertical sides, in the longitudinal direction of the link element 11.
As shown in FIGS. 7 and 8, the link elements 11 are disposed around the pins 20 in a staggered pattern whereby pins 20a to 20d are allowed to cooperate with links 11a to 11e. Specifically, as shown in FIG. 9, links 11f and 11g in the first row engage with pins 20c and 20d at one position, and with pins 20f and 20g at another position. The links in the second row are shifted from the links in the first row in such a manner that a link 11h engages with pins 20a and 20b, a link 11i engages with the pins 20d and 20e, and a link 11j engages with the pin 20g and an adjacent pin (not shown). In the next two rows adjacent to each other, links 11k and 11l engage with the pins 20b and 20c, while links 11m and 11n engage with the pins 20e and 20f. In the following row formed by links 11o, 11p, and 11q, the links are arranged in the same manner as in the second row formed, by the links 11h, 11i, and 11j. In the next two adjacent rows, links 11r and 11t, and links 11s and 11u are arranged in the same manner as the links 11f and 11g in the first row.
FIG. 10 shows the angular orientation of a pin 201 before it enters the pulley between the conical pulley faces. In this state, the axial center 25a of the pin 201 is not yet held between the conical faces, and the lower corner 19c of one projection 16c of the link element 11 is in contact with the lower edge of the flat side surface 23c of the pin 201.
FIG. 11 shows the angular orientation of the pin 201 in which it is gradually coming into contact with the conical pulley. In this state, the upper corner 19d of the projection 16c of the link element 11 is in contact with the upper edge 23d of the surface 23c of the pin 201.
With the first example of the prior art in which, as shown in FIG. 12, a link plate 28 is formed with two pin holes 29, when tensile load F is applied, the portions denoted at Z are deformed outwardly, but the portion X having a relatively high rigidity undergoes substantially no deformation. Consequently, a large moment acts on the portions Y, resulting in the generation of high tensile stress at portions Y1. In this way, excessive stress is concentrated in the vicinity of the upper and lower portions of the two pin holes 29, thereby rendering the conventional belt unable to transmit very large torque.
In contrast, with the construction shown in FIG. 13, in which a link plate 30 is formed with a single opening 31, when tensile load F is applied, the side portions 32 of the link plate 30 are deformed outwardly, and, as this deformation proceeds, the upper and lower edge portions 33 and 34 having a relatively low rigidity are deformed inwardly. Consequently, bending moment at the corner portions 35 and 36 is reduced, and the tensile stress applied to the end faces 37 and 38 at these corners is also reduced.
With the second example of the prior art in FIG. 3, however, concentration of excessive stress occurs at the projections 16a and 16b of the link elements 11 or at the transitional portions 17a and 17b on the sides of the link elements 11, thereby rendering the endless transmission belt unable to transmit large torque.
The link elements 11 are usually formed by stamping them. During stamping, however, broken surfaces tend to be formed in the projections 16a and 16b, the transitional portions 17a and 17b, and portions in the vicinity of these portions of the link elements 11, because the aforementioned portions are relatively narrow and small. Such broken surfaces may often lead to breakage of the link elements 11 as well as to curtailed life of the stamping die, thereby causing an increase in production cost of the link plates.